1. Field of the Invention
The present invention relates to an apparatus for separating moisture, and more particularly water from a glycol regenerator/still which has been removed from, for example, natural gas during the dehydration of same.
2. The Prior Art
Natural gas, when it is drawn from underground sources, often is "contaminated" with water vapor. The presence of such water vapor is undesirable, since it can cause corrosion as well as facilitate hydrate formation in natural gas pipelines.
To remove such water vapor, dehydrators, such as glycol dehydrators have been used to remove the water vapor from the gas. Other forms of dehydrators, which do not absorb the water, or which utilize solutions other than glycol, have also been known in the art.
With respect to the use of glycol, and for example, triethylene glycol, such a solution acts as an absorbent with respect to water vapor. The moist glycol is then later distilled in what is known as a glycol regenerator. After the water is separated from the glycol solution, this "clean" glycol is then reused for further dehydration of natural gas.
Inasmuch as natural gas typically contains various volatile organic compounds (VOCs) such as benzene, toluene, ethyl-benzene, and xylenes (collectively known as BTEX), as well as water, and inasmuch as such organics also become absorbed into the glycol during dehydration, these potentially harmful constituents likewise become separated from the glycol during the distillation process. However, because of the toxicity of the BTEX components and, in turn, the potential danger they may cause if released into the ambient environment, methods have been devised for removing such BTEX from the water during distillation from the glycol solution toward operable safe use of same.
One such system for removing BTEX from recovered water is shown in Lowell, U.S. Pat. No. 5,209,762, the disclosure of which is incorporated herein by reference. In the Lowell '762 system, the water vapor is passed through a condenser having one or more stages which may be air and/or water cooled. The condensate is then collected in a three phase separator, in which the condensate forms in three distinct layers: on bottom, purified liquid water; in the middle, liquid BTEX; on top, gaseous BTEX. The liquid water may then be passed to a series of one or more strippers, and other subsequent polishing stages, to further reduce the amount of BTEX and other undesirable organic constituent compounds. The liquid BTEX is drained off and recovered--inasmuch as BTEX, in liquid form, has viable commercial uses, such as for fuel. The gaseous BTEX is either emitted into the ambient environment, burned off as waste gas flare, or, alternatively, it is added to the fuel gas used to provide the heat for the glycol regenerator. Accordingly, when the gaseous BTEX compounds are combusted, they are broken down into environmentally more acceptable combustion byproducts.
The Lowell '762 glycol dehydration and BTEX separation systems are disclosed and contemplated as being a combined installation. One problem which may arise during the operation of such a system is that the back pressure of the glycol regenerator column may fluctuate and become too great, impeding flow of the glycol through the regenerator, and of the water/BTEX vapor through the regenerator column. In addition, to having possible slowed flow-through the water/BTEX vapor, a secondary effect of such variable, uncontrolled back pressure, is the buildup in the regenerator of various deposits which can further accelerate the impediment of flow-through, and build up of further deposits, as well as contributing to the overall degradation of the regenerator structure.
Indeed, such back pressure may affect the boiling point of the glycol/H.sub.2 O system at a given composition (wherein higher pressure increases the boiling point). Accordingly, this change in the boiling point will 1) increase glycol decomposition, 2) cause corrosion of the firebox tubes, and 3) require more fuel, inasmuch as a higher temperature will be required to distill the glycol.
Accordingly, it would be desirable to provide a glycol dehydration system which would include a BTEX separation system which would have an improved flow-through of water/BTEX vapor from the regenerator to the condenser/accumulator stage.